Refractory article and method of making the same

ABSTRACT

A thermally stable refractory article and method of forming the same is provided. The refractory article comprises a mixture of fine and coarse silica sands containing from trace amounts up to about 10 weight percent alumina and a binder therefor. Preferably the fine silica sand has a particle size ranging from about 0.06 to about 0.10 mm while the coarse silica sand has a particle size of up to about 3.0 mm. The binder is a silica-alumina clay. Preferably it contains in weight percent from about 55 to about 60 percent silica and from about 22 to about 40 percent alumina, plus incidental impurities. 
     The invention also concerns the method of forming the above described refractory article and a monolithic lining therefrom.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a unique unfired refractory article orbrick capable of withstanding temperatures of up to 3,200° F. and abovewhich is characterized by its resistance to thermal shock and generalchemical inertness in a molten metal environment.

Broadly stated, the present invention relates to an improved unfiredrefractory brick which includes a mixture of fine silica sand particleshaving a particle size ranging from about 0.06 mm to about 1.0 mm andcoarse silica sand particles having a particle size of up to about 3.0mm which are bonded together by a clay binder.

2. Description of the Prior Art

It is well known to process or transport molten metals, particularlyiron base metals, in vessels or receptacles which are lined withrefractory materials. For example, in the handling or processing of pigiron it is common practice to line the receiving vessel or ladle withcalcined fire-clay bricks which have an alumina content as high as 35weight percent.

In general, the receiving vessel or ladle is usually provided with arefractory lining which consists of a plurality of individual bricksheld in place by a suitable mortar. While this type of refractory brickperforms well in most instances, it nevertheless suffers from certaininherent deficiencies. For example, often times the mortar is attackedby slag and/or the molten metal being processed. This causes the mortarto erode and results in the formation of so-called "cat-heads", i.e.,the rounding of the surface of the brick in contact with the moltenmetal, on the individual bricks which make up the vessel lining.Ultimately, the molten metal permeates the spacing betweenjuxtapositioned bricks and causes liner failure to occur.

In addition, most refractory brick used for the foregoing purpose tendto shrink when contacted by molten iron based metals. This causes themortar to separate from the brick and permits molten metal to fill theso-formed void. In due course, this causes the lining to fail.

Accordingly, it is the principal object of the present invention toprovide a means for overcoming the before discussed problems byproviding a unique refractory brick.

Other objects of the invention will be apparent to those skilled in theart from a reading of the specification and claims.

SUMMARY OF THE INVENTION

In one aspect, the present invention broadly concerns a thermally stablerefractory article composed of a mixture of special silica sands whichare bonded together by a clay binder. In its preferred embodiment, it iscomposed of a mixture of from about 50 to about 70 weight percent finesilica sand having a particle size ranging from about 0.06 mm to about0.10 mm; from about 10 to about 30 weight percent of a coarse silicasand having a particle size ranging from about 0.2 to about 3.0 mm; andfrom about 15 to about 30 weight percent of a clay binder.

In another aspect, the present invention concerns a method of forming arefractory article which is thermally stable at elevated temperaturescomprising forming a mixture of special silica sands and clay;compacting this mixture into the desired shape; and subjecting thecompacted article to a drying treatment whereby the moisture content ofthe so-formed article ranges, in weight percent, from about 1.5 to about4.0 percent.

In still another aspect, the present invention concerns a method offorming a monolithic lining in a receptacle for receiving molten metalcomprising providing a lining including a plurality of refractoryarticles composed of the above described materials, and heating thelining to a temperature sufficient to cause at least the surface of saidrefractory articles to become plastic thereby causing juxtapositionedrefractory articles to become bonded together in a unitary manner.

Other features and aspects of the present invention will be clear tothose skilled in the art from a reading of the specification and claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Refractory articles, usually in brick form, produced according to thepresent invention are fabricated by forming a mixture of special silicasands and clay. Broadly, this mixture of sands is composed of theappropriate amount of both fine and coarse silica sands. The fine silicasand has a particle size ranging from about 0.06 mm to about 0.10 mm.The coarse sand has a particle size of up to about 3.0 mm. In thepreferred embodiment, both forms of silica sand contain from a traceamount to about 10 weight percent alumina with the remainder beingessentially silica (SiO₂) plus incidental impurities.

The preferred binder is a clay composed of from about 22 to about 40weight percent alumina and from about 55 to about 60 weight percentsilica, plus incidental impurities.

The refractory article of the invention is produced from a mixturecomposed of from about 50 to about 70 weight percent fine silica; fromabout 10 to about 30 weight percent coarse silica; and from about 15 toabout 30 weight percent silica-alumina clay. The above ingredients areso selected that the chemical composition of the resultant article isfrom about 6 to about 9 weight percent alumina with the remainder beingessentially silica plus incidental impurities.

In addition to the foregoing ingredients, the refractory article of theinvention can have other materials added thereto to effect itsproperties and enhance its ability to withstand special conditions thatit may experience in actual use. For example, chemical hardening agentssuch as sodium or other alkali metal phosphates, alumina phosphate, etc.may be added in varying percentages to increase the bonding and hardnessof the fundamental refractory article. This results in an article whichis ideal for use in slag zones or on the bottom of the ladle wheremolten metal has a high tendency to wear or wash away the article orbrick.

The refractory article of the invention was primarily developed to copewith the severe environmental conditions found in iron and steel ladles.That is, the refractory article or brick must be able to withstandtemperatures ranging up to about 3,200° F., sudden changes intemperature (thermal shock) and various stresses, usually compressive.In addition, it must be able to withstand the action of slags, rangingfrom acid to basic in character, and molten metals.

In the preferred embodiment of the invention the refractory article isin the form of a brick which is generally described as an unfired silicabased brick intended for use in ladles for containing molten iron andsteel. The brick of the invention is exceptionally dense, i.e., it has ahigh apparent density. In use, it is employed to line the interiorsurface and bottom of the ladle. When molten metal is introduced intothe ladle, the surface of the lining (made from the unfired brickswithout the use of any mortar) becomes monolithic. That is, because ofthe temperature of the molten metal the bricks expand thus closing thejoints or spacing between them while concurrently the surfaces of thebricks become plastic and cause them to be bonded together. As a resultof this monolithic condition, a lining is obtained which does not havejoints for molten metal to penetrate or attack. Accordingly, the beforediscussed "cat-head" problem associated with conventional linings isavoided.

The refractory article of the invention is produced by forming a mixtureof fine silica sand, coarse silica sand and a clay binder. The chemicalcomposition, ranges of ingredients and physical characteristics of theseindividual components have been discussed hereinbefore and accordinglyfor the sake of brevity will not be discussed hereinafter in detail.

In the manufacture of the article of the invention, water and atemporary binder, for example waterglass, are added to the beforedescribed mixture. The water is added in an amount sufficient to insurethat the raw mixture has a water content ranging from about 3.5 to about6.0 weight percent. The resultant material is then formed into anarticle having the desired apparent density and configuration. In thefabrication of brick, the raw mix is compressed to a degree sufficientto cause the resultant article to have an apparent density of about 2.26g/cc. Thereafter, the resultant article is either air dried or dried bythe application of mild heat (heating at temperatures up to about 220°F. have been utilized successfully) so that the moisture content of thedried article ranges from about 1.5 weight percent on the surface toabout 3 to 4 weight percent on the interior of the article.

Refractory brick produced according to the present invention, as beforenoted, are used to line the side walls and bottoms of ladles. Thesebrick are put in place without the use of any mortar. When contacted bymolten metal, the brick will first shrink slightly. This occurs at atemperature ranging from about 1,000° C. to about 1,300° C. The brickwill then expand approximately 6-7 percent when heated at a temperatureof about 1,500° C.-1,520° C. Above this temperature, the surface of thebrick will become plastic. This plastic surface layer is very thin.However, it is adequate to cause juxtapositioned bricks to be bondedtogether to form a monolithic lining.

The following Example sets forth a typical means of fabricating therefractory articles of the invention.

EXAMPLE

About 1,300 pounds of a raw mixture consisting of, in weight percent,about 60 percent fine silica sand having an average particle sizeranging from about 0.06 to about 0.10 mm, 20 percent coarse silica sandhaving an average particle size ranging from about 0.2 mm up to about3.0 mm, and 20 percent silica-alumina clay were mixed together in aconventional blending apparatus.

Both the fine and coarse silica sands had the same chemical composition,about 90 to about 91 weight percent silica and from about 1.2 to about5.0 weight percent alumina plus incidental impurities.

The binder material, i.e., the clay was composed of about 57.0 weightpercent silica and about 28.5 weight percent alumina, plus variousimpurities.

Water and a temporary binder (waterglass) were then added to the raw mixin such a fashion that the moisture content thereof was about 8.0 weightpercent. A plurality of bricks about 8.0 by 10.0 by 3.0 inches were thenformed from this wet mix. The apparent density of the so-produced brickswas about 2.26 g/cc. The bricks were then dried at a temperature ofabout 200° F. The moisture content of the dried bricks ranged from about1.5 weight percent on the surface to about 3-4 weight percent in thecenter.

The chemical composition of the resultant brick (both sand plus binder)was about 6.5 weight percent alumina with the remainder beingessentially silica plus incidental impurities.

About 700 bricks produced as described above were used to line thebottom of a ladle. These bricks were put in position without the use ofany mortar. About 250 tons of molten iron was poured into the ladle tocause the bricks to fuse together to form a monolithic lining.Subsequently, about 350 more heats of molten iron were poured into theladle before any significant deterioration in the lining was observed.

By way of contrast, when conventional fire-clay bricks were used to linethe same size and type of ladle significant deterioration was noticedafter 200 heats of molten iron were were poured.

From the foregoing, it is clear that a new and superior refractoryarticle or brick has been provided which exhibits desirable propertiesnot found in prior art refractory bricks.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:
 1. An unfired refractory article comprising fromabout 50 to about 70 weight percent fine silica sand particles, saidfine silica sand particles having an average particle size ranging fromabout 0.06 to about 0.10 mm.; from about 10 to about 30 weight percentcoarse silica sand particles, said coarse silica sand particles having amaximum particle size of about 3.0 mm.; and from about 15 to about 30weight percent of an alumina containing clay binder, with the totalcontent of alumina in said unfired article ranging from about 6.0 toabout 9.0 weight percent.
 2. A method for forming a unfired silica baserefractory article which is characterized by having a positivecoefficient of thermal expansion at a temperature of about 1500° C.which comprises:forming a mixture comprising from about 50 to about 70weight percent fine silica sand particles with said fine silica sandparticles having an average particle size ranging from about 0.06 toabout 0.10 mm., from about 10 to about 30 weight percent coarse silicasand particles with said coarse silica sand particles having a maximumparticle size of about 3.0 mm., and from about 15 to about 30 weightpercent of an alumina containing clay binder, with the total content ofalumina in said unfired article ranging from about 6.0 to about 9.0weight percent; compacting said mixture to a degree sufficient to causethe resultant article to have a density in excess of about 2.26; andsubjecting said compacted article to a drying treatment whereby themoisture content of the so-formed article ranges, in weight percent,from about 1.5 to about 4.0 percent.
 3. The article of claim 1 whereinsaid clay binder consists essentially of a mixture of silica andalumina.
 4. The article of claim 3 wherein said binder, in weightpercent, is composed of from about 55 to about 60 percent silica andfrom about 22 to about 40 percent alumina, plus incidental impurities.5. The article of claim 1 wherein said fine silica sand particles arepresent, in weight percent, in an amount of about 60 percent; saidcoarse silica sand particles are present, in weight percent, in anamount of about 20 percent; and said clay is present, in weight percent,in an amount of about 20 percent.
 6. The article of claim 1 which isfurther characterized by having a moisture content, in weight percent,ranging from about 1.5 to about 4 percent.
 7. The method of claim 2wherein said clay binder consists essentially of a mixture of silica andalumina.
 8. The method of claim 7 wherein said binder, in weightpercent, is composed of from about 55 to about 60 percent silica andfrom about 22 to about 40 percent alumina, plus incidental impurities.9. The method of claim 2 wherein said fine silica sand particles arepresent, in weight percent, in an amount of about 60 percent; saidcoarse silica sand particles are present, in weight percent, in anamount of about 20 percent; and said clay is present, in weight percent,in an amount of about 20 percent.